This invention relates to mechanical override systems to operate vehicle drive trains normally governed by an on-board computer.
In recent years, many vehicle drive trains have been proposed having electronic means to govern the operation of an engine and automatic transmission. One such drive train is that found in an M1 or M1A1 combat tank presently used by the U.S. Army. These tanks have an electronic control unit, commonly called an ECU, which governs the fuel injection system. These tanks also have a transmission shift selector which electrically actuates solenoid valves to regulate an automatic transmission.
The fuel injection system on these tanks is referred to as a hydromechanical unit or HMU, the system being an assembly of electrically actuatable valves and other components. It is contemplated that certain kinds of battle damage to the tank will disable the ECU or HMU. If the HMU experiences a power failure, the HMU reverts to a flow reducing mode during which the engine runs at only 5% of its power capacity and the tank can move at only 1 mph. If the HMU does not receive control signals from the ECU, the HMU will revert to the flow reducing mode. In addition, if the ECU detects certain suboptimal operating conditions in the engine, the ECU signals the HMU to enter the flow reducing configuration. It is also contemplated that electrical communication between the shift selector and the automatic transmission can be interrupted by battle damage or other causes.
In many situations, such as tank crew training exercises, the HMU's entry into the flow reducing mode or failure of the ECU does not pose serious problems. In such situations, limiting fuel flow is a prudent means to reduce the risk of damage to the engine. However, in battle or emergency situations, the need to extricate the tank and its crew from danger supersedes concerns for the engine. To provide tank maneuverability in such situations, we propose an entirely nonelectrical system for overriding the ECU, for manually shifting the automatic transmission, and for bypassing the fuel flow restriction in the HMU.
The override system includes a first linkage which mechanically operates valves regulating the transmission. The system has a second linkage which operates a fuel bypass valve hydraulically in parallel with a flow control valve in the HMU. The linkages are controlled by manually actuated members on a control assembly in the driver's compartment of the tank. The control assembly has a means for preventing the members from being moved independently of one another, so the transmission can not be shifted when the engine is running above a certain speed. The preventing means also keeps the bypass valve from being opened unless the overriding system places the transmission in the drive or reverse mode.